Impact on Walking Performance Was Modest

The study was small, with just 20 participants. And the effect was modest, with the dark chocolate consumers showing an 11% increase in maximal walking distance compared with no change in patients who ate equal amounts of milk chocolate.

Loffredo and colleagues called the research a "proof-of-concept" study, adding that bigger studies with longer follow-up times are needed to confirm the findings.

Natalie Evans, MD, of the Cleveland Clinic, who was not involved with the study, said further research is warranted.

"The study was really small, so I think it is hard to know how significant ultimately this will be," she said, adding that restricting the study population to patients with intermittent claudication (IC) was another limitation.

"There is a huge population out there with peripheral artery disease, but only about 11% of them actually have intermittent claudication," she said. "I think it would be really interesting to find out what impact dark chocolate would have on [patients without this complication]."

The goal of the Loffredo group's latest work was to determine whether eating dark chocolate could improve walking autonomy in PAD patients with IC.

The single, blind, crossover study included 20 patients (14 males, 6 females) who routinely exhibited IC symptoms after walking less than 200 meters (Fontaine stage IIb) and who were in stable condition without abrupt changes in walking distance and ankle brachial index (ABI) in the month prior to entry.

The patients were randomized to "treatment" with 40 grams of dark chocolate (>85% cocoa) or milk chocolate (<35% cocoa) in a crossover, single-blind design, with at least 1 week of washout between the study's two phases.

“Who wouldn't want to eat dark chocolate to feel better?"

Flow-mediated dilation (FMD), oxidative stress, serum levels of NOx and epicatechin (EC) were assessed at baseline, after 24 hours' abstinence from food rich in polyphenols, and 2 hours after ingestion of chocolate.

Fasting blood samples were drawn and analyzed early in the morning (8 a.m.) and ABI and FMD were also performed. At 9 a.m. a first treadmill test was performed and 2 minutes after maximal walking distance (MWD) and maximal walking time (MWT) were measured, ABI was measured again.

At 9:25 a.m. the participants were given the chocolate (40 grams), and they had 15 minutes to eat it. At 11:25 a.m. blood samples were again drawn to analyze oxidative stress and epicatechin levels. At 11:30 a.m. a second ABI at rest and FMD were performed, and at 11:50 a.m. the participants underwent a second treadmill test. Once again, ABI was performed 2 minutes after MWD and MWT were measured.

Researchers: 'Clinical Implications Limited'

Dark chocolate consumption was found to significantly increase MWD, MWT, and serum NOx, and it decreased serum isoprostanes and sNOX2-dp, which is a marker of blood NOX2 activity.

None of these changes were observed in the patients who consumed the milk chocolate.

"Serum epicatechin and its methylated metabolite significantly increased only after dark chocolate ingestion," the researchers wrote.

Multiple linear regression analysis showed that change in MWD was independently associated with change in MWT and change in NOx. In vitro research demonstrated that HUVEC incubated with a mixture of polyphenols significantly increased nitric oxide and decreased E-selectin and VCAM1.

"This study has implications and limitations," the researchers wrote. "It should be considered a proof-of-concept study that is potentially useful to understand the mechanism of disease related to IC but not transferable to clinical practice because of small sample size and the disease of the study."

Exercise Also Works Well

American Heart Association spokesman Mark Creager, MD, said although the preliminary findings were positive, the impact of the chocolate intervention was still only about one-tenth that of the most effective known interventional treatment for IC related to PAD -- regular exercise.

"It seems paradoxical to tell people who have pain when they walk, to walk, but exercise has been shown to be extremely effective in these patients," Creager, of Harvard Medical School and Brigham & Women's Hospital, both in Boston, told MedPage Today. "We know that PAD patients who train for 3 months under supervision at least three times a week for about 45 minutes can double their walking distance."

He added that exercise appears to improve the metabolic function of the skeletal muscles and there is some evidence that it may even promote the development of new blood vessels. It may also simply help improve function and help train patients to walk better.

While Creager and Evans called the latest research interesting, both said it is too soon to recommend chocolate therapy to PAD patients.

"Who wouldn't want to eat dark chocolate to feel better?" Evans said. "But I think there is a lot more bang for your buck in terms of managing traditional risk factors for PAD." This includes convincing PAD patients who smoke to kick the habit and urging them to maintain a healthy weight so they don't develop diabetes, she said.

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